The problem might be related with the audio file formats you are trying to play on Internet Explorer 9.
I've been working on playing audio on web pages using HTML5 for a while.
Please check HTM5 tutorial showing how to play audio on HTML5
But if you do not hear the sound you expect to hear on Internet Explorer 9 (IE9), the cause of the problem is probably because Internet Explorer web browser does not support that audio file format on HTML5
You can convert sound file format or use an other sound file that Internet Explorer 9 web browser support